Ischemic acute renal failure (ARF) remains the primary cause of ARF with unacceptably high morbidity and mortality and attendant acute and chronic health care costs. Proximal tubule cell injury has become the focus the focus of ischemic ARF investigation and recent data point to an important pathophysiologic role of actin cytoskeletal alterations in proximal tubule cell injury. However, mechanistic data defining how ischemic cell injury leads to actin cytoskeletal alterations are lacking. Therefore, we have assembled a highly interactive, scientifically diverse team to evaluate the mechanisms and effects of ischemia-induced actin alteration. Our central hypothesis states that cellular ATP depletion results in dysregulation of the actin cytoskeleton resulting in surface membrane, junctional complex and cell polarity abnormalities. Specifically, we hypothesize unregulated actin polymerization occurs secondary to direct effects of the ATP/ADP ratio on the G-actin nucleotide pool and actin-binding protein affinity and interactions. Furthermore, we postulate ischemia results in inactivation of Rho GTPases leading to F-actin delocalization and disruption of the cytoskeletal-membrane infrastructure necessary for maintenance of cell- cell junctional complexes, cell polarity, Golgi apparatus and polarized targeting machinery. To directly investigate these interrelated hypotheses we have developed and implemented a myriad of quantitative biochemical, imaging, and molecular techniques that will directly identify and quality the mechanisms and effects of ischemia-induced actin dysregulation at the single cell level. Central to out thematic approach is the use of quantitative image processing and 3-D reconstructions using both confocal and wide field microscopic applications and confirmatory standard EM and immunogold techniques.